1. Field of the Invention
The present invention relates to a roll cover apparatus for covering a roll of a papermaking machine. More particularly, the present invention relates to a roll cover apparatus for a press section or calender section.
2. Information Disclosure Statement
In the papermaking industry, a web of paper from a forming section is typically guided through at least one press nip for removing further quantities of water from the formed web. Such press nips have, in the past, included a pair of counter-rotating steel rolls or a steel roll cooperating with a counter-rotating granite roll or the like.
In certain applications, it has been found advantageous to cover the steel roll with a compliant cover for improving the surface characteristics of the resultant pressed web.
Although various rubber compositions have been used in the fabrication of roll covers, polymeric materials have been used very successfully in the manufacture of such roll covers.
The aforementioned polymeric materials may be reinforced with woven or non-woven fabric and may comprise single or multiple layers.
Often the outer face of the cover is grooved in order to assist in channeling water away from the press nip.
Additionally, roll covers have been used in the calendering of a web downstream from the press section.
Normally, a web of paper or liner board extends around a plurality of drying cylinders downstream relative to the press section. Subsequently, the dried web extends through a calender for imparting smoothness to the surface of the web. Such smoothing could be likened to the ironing of domestic clothing in order to smooth the surface thereof.
Although many calenders include a stack of counter-rotating steel rolls, more recently, soft calendering has found wide application in the papermaking art.
Soft calendering essentially includes passing a web of paper through a calendering nip defined between a steel surfaced roll and a compliant cover of a mating roll.
In both the press section and the calendering section of a papermaking machine, a problem has existed in that when even slight slippage occurs between the web of paper and the roll cover, such slippage generates an electrostatic charge on the roll cover surface. Such is particularly a problem in a dry ambient atmosphere.
In order to compensate for the aforementioned generation of such electrostatic charge due to the microslippage between the web and the roll cover, various electrical conductors have been employed for dissipating the electrostatic charge from the surface of the roll cover.
The aforementioned conductors include metallic tinsel or silver paper arranged such that the tinsel bears against the outer surface of the rotating roll cover. Such tinsel conducts an electrical current from the surface of the roll cover so that the cover charge can be dissipated to ground.
However, the silver paper or tinsel is very thin, and in the event of the tinsel breaking away from the main body of the tinsel conductor, not only does such piece of tinsel become attached to the web, but also that portion of the roll cover adjacent to where such breakage occurred is no longer subjected to electrostatic discharge. Consequently, an electrostatic charge can build up on the surface of the roll and such charge can intermittently discharge from the roll cover through the web to ground through the cooperating steel roll of the press or calendering nip.
Such dissipation through the web causes a scorch mark on the web which renders the resultant web unsuitable for printing thereon.
The present invention seeks to overcome the aforementioned disadvantages of the aforementioned proposals by providing electrically conductive fibers and reinforcement randomly dispersed within the roll cover for conducting the current to dissipate the electrostatic charge on the surface through the roll cover to the electrically conductive roll on which the roll cover is formed.
Therefore, it is a primary objective of the present invention to provide a roll cover apparatus that overcomes the aforementioned inadequacies of the prior art proposals and which makes a considerable contribution to the art of dissipating an electrostatic charge on a roll cover.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description taken in conjunction with the annexed drawings.